1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Ground Loop Question on Grounding Shielded Cavities

Discussion in 'Tele-Technical' started by TonyNJ, Apr 16, 2021.

  1. TonyNJ

    TonyNJ TDPRI Member

    Age:
    36
    Posts:
    19
    Joined:
    Apr 10, 2021
    Location:
    New Jersey USA
    I painted the neck/bridge cavities in an MG chemicals silver/copper paint.

    For the neck I'm running a wire from the base of the cavity to the main ground in the base of the control cavity. I will make sure any exposed leads on the neck pickup do not contact the wall of the cavity.

    For the bridge cavity, I'm also planning to run a wire between the cavity and the base of the control cavity. The bridge pickup will be grounded to the bridge by metal/metal contact from the screws and the bridge pickup grounded directly to the volume pot. The standard ground will also run from the volume pot to the base of the control cavity (main ground lug connecting the bridge/neck cavities as well).

    However, if the bridge also makes contact with conductive paint that may have spilled (a little) over the edge of the bridge cavity, would that create a ground loop? Same question for the main control cavity.

    Thanks, and have a good weekend all!
     
  2. chezdeluxe

    chezdeluxe Poster Extraordinaire

    Age:
    71
    Posts:
    9,849
    Joined:
    Dec 29, 2007
    Location:
    Brisbane Australia
    There is no such problem as a ground loop in a guitar.
     
    teleplayr, Peegoo, Deaf Eddie and 2 others like this.
  3. Peegoo

    Peegoo Poster Extraordinaire

    Posts:
    8,134
    Joined:
    Oct 11, 2019
    Location:
    Between the Raindrops
    Therre's nothing to worry about.

    The myth of a ground loop in a guitar came from the ground loop problem in amplifiers.

    Amp circuits use several DC voltage levels and this results in differentials in ground potential. These differing ground potentials in various stages of the circuit can cause current flow from one ground to another, creating noise in the circuit. Measures need to be taken to prevent this ocurring in an amp.

    In a passive guitar circuit, there is only one voltage source and current, and that is the AC from the pickups. This makes a ground loop impossible because of the extremely low voltage and current in a guitar circuit. Multiple paths to ground are perfectly fine because all grounds are at the same potential.

    A ground loop can occur in an AC circuit; it is caused by magnetic field induction from one conductor to an adjacent one. However, this condition requires much higher voltages and current levels than what a guitar circuit is capable of producing.
     
    Deaf Eddie, moosie, dougstrum and 5 others like this.
  4. TonyNJ

    TonyNJ TDPRI Member

    Age:
    36
    Posts:
    19
    Joined:
    Apr 10, 2021
    Location:
    New Jersey USA
    Thanks a lot fellas!
     
    Peegoo likes this.
  5. maj34

    maj34 Tele-Holic

    Posts:
    505
    Joined:
    Nov 19, 2013
    Location:
    St. John's, NL, Canada
    My opinion: ground loops can exist but are of minimal impact in a guitar due to the low currents involved.

    According to Wikipedia:
    "In an electrical system, a ground loop or earth loop occurs when two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them."

    Also:
    "Wikipedia is the best thing ever. Anyone in the world can write anything they want about any subject, so you know you are getting the best possible information."
    - Michael Scott

    That said, I had a guitar that had one of the worse case scenarios and the shielding worked just fine. I used stew mac copper shielding tape and after a few years all the patches of copper are showing 10s of ohms. Can't trust that adhesive IME. I soldered them all together and noticed... no difference in sound. And I was "lucky enough" to be living in a 100 year old house with single conductor ceramically insulated wiring, a great test bed for testing with noise.

    But if you're taking the time to shield your guitar (and I'm of the opinion that it's very worthwhile on single coils) you may as well do it right. All points have a single path to ground and only exception for me is when I have a poor unavoidable ground, I'll add a solidly bonded ground.

    OP: I wouldn't stress about it at all, but I would also just make sure there's no conductive paint anywhere I don't want it. If the area is not visible I might even hit it with 400 then 600 sandpaper, but then again I'm just going through a sanding phase since I got micromesh. I also try to avoid bare conductors touching shielding. I don't think it's necessary to do so, but while I'm at it, and for half a cent worth of electrical tape...
     
    Last edited: Apr 17, 2021
  6. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    64
    Posts:
    17,904
    Joined:
    Jul 18, 2010
    Location:
    Western Connecticut
    TonyNJ likes this.
  7. TonyNJ

    TonyNJ TDPRI Member

    Age:
    36
    Posts:
    19
    Joined:
    Apr 10, 2021
    Location:
    New Jersey USA
    Only real concern was the bridge contacting any TINY bit of conductive paint I may have brushed over the edge. I suppose I could forgo running a wire from the base of the bridge pickup cavity to the base of the control cavity, and instead just run a wire from the base of the bridge cavity to the bridge itself (crush between bridge and body technique).

    I guess the same issue might apply for the control plate, since it is aluminum and will be grounded to a lug at its base. The tiniest amount of conductive paint may have made it over the edge (yes, I'm crazy anal about stuff).

    For the forward cavity I'm pickguard mounting the pickup, grounding it separately to the electronics, and running a wire from the base of the pickup cavity to the base of the control cavity where I will connect all grounds.

    Mostly I want to just go with what @Peegoo says, that way I can just go with my original plan ;)

    20210418_115411.jpg
     
  8. Peegoo

    Peegoo Poster Extraordinaire

    Posts:
    8,134
    Joined:
    Oct 11, 2019
    Location:
    Between the Raindrops
    You want the plates to be in contact with the conductive paint for maximum effectiveness of the shielding.
     
    schmee likes this.
  9. schmee

    schmee Doctor of Teleocity

    Posts:
    14,954
    Joined:
    Jun 2, 2003
    Location:
    northwest
    ^^ What he said. And put metal/tape under the pickguard so it grounds also.
     
  10. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    64
    Posts:
    17,904
    Joined:
    Jul 18, 2010
    Location:
    Western Connecticut
    Let's be very clear on this point: ALL shielding in a guitar MUST be grounded. Even if it doesn't know it's shielding. Such as a random loose bit of metal, or snip of wire.

    Ungrounded metal will create some very weird noise issues. Often intermittent, but always annoying and can be a bear to diagnose. Double check all those shield grounds.
     
  11. TonyNJ

    TonyNJ TDPRI Member

    Age:
    36
    Posts:
    19
    Joined:
    Apr 10, 2021
    Location:
    New Jersey USA
    Well, DONE! No noise, no issues. Sweet cavalier pickups from my state.

    SVP_9079.jpg SVP_9080.jpg SVP_9082.jpg SVP_9083.jpg SVP_9084.jpg SVP_9086.jpg SVP_9091.jpg SVP_9092.jpg SVP_9096.jpg SVP_9102.jpg
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.